The presence of water in small quantities in gaseous hydrocarbons is harmful to industrial processes and the monitoring of moisture content is necessary to assure proper results. The aluminum oxide hygrometer is very good for measuring very low levels of moisture in gases and some liquids if the sample is not harmful toward aluminum or aluminum oxide. The P.sub.2 O.sub.5 hygrometer is somewhat less sensitive but very useful for many more harmful gas samples encountered in chemical plants. However, some samples are disruptive of the P.sub.2 O.sub.5 hygrometer. HCl in concentration above 1% gives a background reading because the HCl is partially electrolyzed. For such samples that contain very low ranges of moisture, the signal from the P.sub.2 O.sub.5 hygrometer is low and subject to considerable uncertainty. The levels of moisture which are of concern generally are in the range of 2 to 50 parts per million (ppm).
U.S. Pat. No. 3,257,609 discloses the use of an adsorption column to selectively separate and accumulate moisture from gaseous hydrocarbon samples followed by desorption and analysis with a hygrometer. U.S. Pat. No. 3,257,609 specifically teaches the use of polyethylene and propropylene glycols on Chromosorb (an agglomerated diatomaceous earth) to adsorb moisture from a process sample. Desorption is accomplished by passing an electrical current through the column to raise the temperature.
U.S. Pat. Nos. 3,263,493 and 3,335,367 disclose the use of gas chromatography columns to separate moisture from gaseous hydrocarbon samples prior to the analysis of the moisture laden fraction with a hygrometer. The hygrometer is conditioned with dry carrier gas when the moisture laden fraction of the sample is not exiting the column.
The use of chromatography columns to accumulate a volume of sample requires knowledge of the flow through the accumulator during the load interval. Thus, sample flow rate and load time must be controlled.